PROJECT 1 DESCRIPTION: Development of an effective AIDS vaccine represents the single best hope for curtailing the human devastation wrought by the AIDS pandemic. Recombinant vectors derived from Modified Vaccinia Virus Ankara (MVA) have become attractive AIDS vaccine candidates because of their safety and demonstrated immunogenicity in heterologous prime-boost immunization regimens in idealized non-human primate models. However, current rMVA-based AIDS vaccines exhibit significant limitations in their abilities to both prime HIV-specific immune responses and to boost such responses following homologous booster immunizations. These limitations likely reflect both the antigenic complexity posed by current rMVA vectors (that effectively dilute HIV-specific immune responses) as well as the generation of significant neutralizing antibody responses that are directed against the vector itself (thereby preventing immunological boosting of desired HIV-specific immune responses upon re-vaccination). Based on our preliminary studies, we hypothesize that the immunogenicity of MVA-based AIDS vaccines may be significantly enhanced by augmenting key beneficial interactions between rMVA vectors and dendritic cells (the most potent antigen-presenting cells in vivo). In a hypothesis driven-manner, we propose to study a number of rational "modifications of rMVA vectors that include (1) expression of chemokines and cytokines to recruit/activate DCs to sites of immunization, (2) deletion of essential viral genes, expression of anti-apoptotic genes, or physicochemical inactivation of rMVA to modulate apoptosis of infected DCs and non-APCs, and (3) deletion of residual poxvirus immune evasion genes from the MVA genome to enhance vaccine immunogenicity. The immunogenicity of such novel rMVA vectors, which simultaneously express multiple HIV consensus antigens representing HIV subtypes B and C, will be evaluated through systematic detailed characterization of cellular and humoral immune responses following immunization of rhesus macaques.